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High cardiorespiratory fitness and exercise show evidence of altering bile acid (BA) metabolism and are known to protect or treat diet-induced hepatic steatosis, respectively. Here, we tested the hypothesis that high intrinsic aerobic capacity and exercise both increase hepatic BA synthesis measured by the incorporation of 2 H 2 O. We also leveraged mice with inducible liver-specific deletion of Cyp7a1 (LCyp7a1KO), which encodes the rate-limiting enzyme for BA synthesis, to test if exercise-induced BA synthesis is critical for exercise to reduce hepatic steatosis. The synthesis of hepatic BA, cholesterol, and de novo lipogenesis was measured in rats bred for either high (HCR) vs. low (LCR) aerobic capacity consuming acute and chronic high-fat diets. HCR rats had increased synthesis of cholesterol and certain BA species in the liver compared to LCR rats. We also found that chronic exercise with voluntary wheel running (VWR) (4 weeks) increased newly synthesized BAs of specific species in male C57BL/6J mice compared to sedentary mice. Loss of Cyp7a1 resulted in fewer new BAs and increased liver triglycerides compared to controls after a 10-week high-fat diet. Additionally, exercise via VWR for 4 weeks effectively reduced hepatic triglycerides in the high-fat diet-fed control male and female mice as expected; however, exercise in LCyp7a1KO mice did not lower liver triglycerides in either sex. These results show that aerobic capacity and exercise increase hepatic BA metabolism, which may be critical for combatting hepatic steatosis.

Low aerobic capacity is strongly associated with all-cause mortality and risk for Alzheimer's disease (AD). Individuals with early dementia and AD have lower aerobic capacity compared to age-matched controls. The mechanism by which aerobic capacity influences AD risk is unknown but is likely mediated by sexual dimorphism and tissue-level differences in mitochondrial energetics. Here, we used rats selectively bred for large differences in intrinsic aerobic exercise capacity. Brain tissue from 18-month and 24-month-old female and male low-capacity runner (LCR) and high-capacity runner (HCR) rats were analyzed for markers of mitochondrial function and AD-associated pathologies. LCR rats, irrespective of sex, exhibited a greater increase in brain amyloid beta (Aβ 42 ) and tau hyperphosphorylation (pTau thr181 /total tau) with aging. In female LCR rats, brain mitochondrial respiration at states 3, 4, and FCCP-induced uncoupling, when stimulated with pyruvate/malate, was reduced at 18 and 24 months, leading to lower ATP-linked mitochondrial respiration compared to mitochondria from HCR rats. Male LCR rats also showed reduced complex II-stimulated mitochondrial respiration (succinate + rotenone) at 24 months compared to HCR rats. Differences in mitochondrial respiration were associated with tau hyperphosphorylation and Aβ42 alterations in both HCR and LCR strains. Proteomic analysis unveiled a distinct difference in the mitochondrial proteome, wherein female LCR rats displayed diminished mitochondrial translation and oxidative phosphorylation (OXPHOS) proteins at 18 months compared to female HCR rats. Conversely, male LCR rats exhibited increased OXPHOS protein abundance but reduced tricarboxylic acid (TCA) cycle proteins compared to male HCR rats. These findings underscore a robust association between intrinsic aerobic exercise capacity, brain mitochondrial function, and AD pathologies during aging., (© 2024. The Author(s).)

Age-associated declines in aerobic capacity promote the development of various metabolic diseases. In rats selectively bred for high/low intrinsic aerobic capacity, greater aerobic capacity reduces susceptibility to metabolic disease while increasing longevity. However, little remains known how intrinsic aerobic capacity protects against metabolic disease, particularly with aging. Here, we tested the effects of aging and intrinsic aerobic capacity on systemic energy expenditure, metabolic flexibility and mitochondrial protein synthesis rates using 24-month-old low-capacity (LCR) or high-capacity runner (HCR) rats. Rats were fed low-fat diet (LFD) or high-fat diet (HFD) for eight weeks, with energy expenditure (EE) and metabolic flexibility assessed utilizing indirect calorimetry during a 48 h fast/re-feeding metabolic challenge. Deuterium oxide (D2O) labeling was used to assess mitochondrial protein fraction synthesis rates (FSR) over a 7-day period. HCR rats possessed greater EE during the metabolic challenge. Interestingly, HFD induced changes in respiratory exchange ratio (RER) in male and female rats, while HCR female rat RER was largely unaffected by diet. In addition, analysis of protein FSR in skeletal muscle, brain, and liver mitochondria showed tissue-specific adaptations between HCR and LCR rats. While brain and liver protein FSR were altered by aerobic capacity and diet, these effects were less apparent in skeletal muscle. Overall, we provide evidence that greater aerobic capacity promotes elevated EE in an aged state, while also regulating metabolic flexibility in a sex-dependent manner. Modulation of mitochondrial protein FSR by aerobic capacity is tissue-specific with aging, likely due to differential energetic requirements by each tissue., (© 2023. The Author(s), under exclusive licence to American Aging Association.)

Mitochondrial quality control processes are essential in governing mitochondrial integrity and function. The purpose of the study was to examine the effects of 10 weeks of high-intensity interval training (HIIT) on the regulatory protein machinery of skeletal muscle mitochondrial quality control and whole-body glucose homeostasis in diet-induced obese mice. Male C57BL/6 mice were assigned to low-fat diet (LFD) or high-fat diet (HFD) group. After 10 weeks, HFD-fed mice were divided into sedentary and HIIT (HFD + HIIT) groups for another 10 weeks ( n  = 9/group). Graded exercise test, glucose and insulin tolerance tests, mitochondrial respiration, and protein markers of mitochondrial quality control processes were determined. HFD-fed mice exhibited lower ADP-stimulated mitochondrial respiration ( p  < 0.05). However, 10 weeks of HIIT prevented this impairment ( p  < 0.05). Importantly, the ratio of Drp1(Ser 616 ) over Drp1(Ser 637 ) phosphorylation, an indicator of mitochondrial fission, was significantly higher in HFD-fed mice ( p  < 0.05), but such increase was attenuated in HFD-HIIT compared to HFD (-35.7%, p  < 0.05). Regarding autophagy, skeletal muscle p62 content was lower in the HFD group than the LFD group (-35.1%, p  < 0.05); however, such reduction was disappeared in the HFD + HIIT group. In addition, LC3B II/I ratio was higher in the HFD group than the LFD group (15.5%, p  < 0.05) but was ameliorated in the HFD + HIIT group (-29.9%, p  < 0.05). Overall, our study demonstrated that 10 weeks of HIIT was effective in improving skeletal muscle mitochondrial respiration and the regulatory protein machinery of mitochondrial quality control in diet-induced obese mice through the alterations of mitochondrial fission protein Drp1 phosphorylations and p62/LC3B-mediated regulatory machinery of autophagy., Competing Interests: The authors declare there are no competing interests.

High versus low aerobic capacity significantly impacts the risk for metabolic diseases. Rats selectively bred for high or low intrinsic aerobic capacity differently modify hepatic bile acid metabolism in response to high-fat diets (HFDs). Here we tested if a bile acid sequestrant would alter hepatic and whole body metabolism differently in rats with high and low aerobic capacity fed a 1-wk HFD. Male rats (8 mo of age) that were artificially selected to be high (HCR) and low-capacity runners (LCR) with divergent intrinsic aerobic capacities were transitioned from a low-fat diet (LFD, 10% fat) to an HFD (45% fat) with or without a bile acid sequestrant (BA-Seq, 2% cholestyramine resin) for 7 days while maintained in an indirect calorimetry system. HFD + BA-Seq increased fecal excretion of lipids and bile acids and prevented weight and fat mass gain in both strains. Interestingly, HCR rats had increased adaptability to enhance fecal bile acid and lipid loss, resulting in more significant energy loss than their LCR counterpart. In addition, BA-Seq induced a greater expression of hepatic CYP7A1 gene expression, the rate-limiting enzyme of bile acid synthesis in HCR rats both on HFD and HFD + BA-Seq diets. HCR displayed a more significant reduction of RQ in response to HFD than LCR, but HFD + BA-Seq lowered RQ in both groups compared with HFD alone, demonstrating a pronounced impact on metabolic flexibility. In conclusion, BA-Seq provides uniform metabolic benefits for metabolic flexibility and adiposity, but rats with higher aerobic capacity display adaptability for hepatic bile acid metabolism. NEW & NOTEWORTHY The administration of bile acid sequestrant (BA-Seq) has uniform metabolic benefits in terms of metabolic flexibility and adiposity in rats with high and low aerobic capacity. However, rats with higher aerobic capacity demonstrate greater adaptability in hepatic bile acid metabolism, resulting in increased fecal bile acid and lipid loss, as well as enhanced fecal energy loss.

Objective: Dynamin-related protein 1 (Drp1) is the key regulator of mitochondrial fission. We and others have reported a strong correlation between enhanced Drp1 activity and impaired skeletal muscle insulin sensitivity. This study aimed to determine whether Drp1 directly regulates skeletal muscle insulin sensitivity and whole-body glucose homeostasis., Methods: We employed tamoxifen-inducible skeletal muscle-specific heterozygous Drp1 knockout mice (mDrp1 +/- ). Male mDrp1 +/- and wildtype (WT) mice were fed with either a high-fat diet (HFD) or low-fat diet (LFD) for four weeks, followed by tamoxifen injections for five consecutive days, and remained on their respective diet for another four weeks. In addition, we used primary human skeletal muscle cells (HSkMC) from lean, insulin-sensitive, and severely obese, insulin-resistant humans and transfected the cells with either a Drp1 shRNA (shDrp1) or scramble shRNA construct. Skeletal muscle and whole-body insulin sensitivity, skeletal muscle insulin signaling, mitochondrial network morphology, respiration, and H 2 O 2 production were measured., Results: Partial deletion of the Drp1 gene in skeletal muscle led to improved whole-body glucose tolerance and insulin sensitivity (P < 0.05) in diet-induced obese, insulin-resistant mice but not in lean mice. Analyses of mitochondrial structure and function revealed that the partial deletion of the Drp1 gene restored mitochondrial dynamics, improved mitochondrial morphology, and reduced mitochondrial Complex I- and II-derived H 2 O 2 (P < 0.05) under the condition of diet-induced obesity. In addition, partial deletion of Drp1 in skeletal muscle resulted in elevated circulating FGF21 (P < 0.05) and in a trend towards increase of FGF21 expression in skeletal muscle tissue (P = 0.095). In primary myotubes derived from severely obese, insulin-resistant humans, ShRNA-induced-knockdown of Drp1 resulted in enhanced insulin signaling, insulin-stimulated glucose uptake and reduced cellular reactive oxygen species (ROS) content compared to the shScramble-treated myotubes from the same donors (P < 0.05)., Conclusion: These data demonstrate that partial loss of skeletal muscle-specific Drp1 expression is sufficient to improve whole-body glucose homeostasis and insulin sensitivity under obese, insulin-resistant conditions, which may be, at least in part, due to reduced mitochondrial H 2 O 2 production. In addition, our findings revealed divergent effects of Drp1 on whole-body metabolism under lean healthy or obese insulin-resistant conditions in mice., Competing Interests: Declaration of competing interest K.Z. receives grant funding from Remedium Bio, but not relevant to this article. No other potential conflicts of interest were reported., (Copyright © 2023 The Author(s). Published by Elsevier GmbH.. All rights reserved.)

Exercise is a physiological stress that disrupts tissue and cellular homeostasis while enhancing systemic metabolic energy demand mainly through the increased workload of skeletal muscle. Although the extensive focus has been on skeletal muscle adaptations to exercise, the liver senses these disruptions in metabolic energy homeostasis and responds to provide the required substrates to sustain increased demand. Hepatic metabolic flexibility is an energetically costly process that requires continuous mitochondrial production of the cellular currency ATP. To do so, the liver must maintain a healthy functioning mitochondrial pool, attained through well-regulated and dynamic processes. Intriguingly, some of these responses are sex-dependent. This mini-review examines the hepatic mitochondrial adaptations to exercise with a focus on sexual dimorphism.

Background: Skeletal muscle from lean and obese subjects elicits differential adaptations in response to exercise/muscle contractions. In order to determine whether obesity alters the adaptations in mitochondrial dynamics in response to exercise/muscle contractions and whether any of these distinct adaptations are linked to alterations in insulin sensitivity, we compared the effects of electrical pulse stimulation (EPS) on mitochondrial network structure and regulatory proteins in mitochondrial dynamics in myotubes from lean humans and humans with severe obesity and evaluated the correlations between these regulatory proteins and insulin signaling., Methods: Myotubes from human skeletal muscle cells obtained from lean humans (body mass index, 23.8 ± 1.67 kg·m-2) and humans with severer obesity (45.5 ± 2.26 kg·m-2; n = 8 per group) were electrically stimulated for 24 h. Four hours after EPS, mitochondrial network structure, protein markers of insulin signaling, and mitochondrial dynamics were assessed., Results: EPS enhanced insulin-stimulated AktSer473 phosphorylation, reduced the number of nonnetworked individual mitochondria, and increased the mitochondrial network size in both groups (P < 0.05). Mitochondrial fusion marker mitofusin 2 was significantly increased in myotubes from the lean subjects (P < 0.05) but reduced in subjects with severe obesity (P < 0.05). In contrast, fission marker dynamin-related protein 1 (Drp1Ser616) was reduced in myotubes from subjects with severe obesity (P < 0.05) but remained unchanged in lean subjects. Reductions in DrpSer616 phosphorylation were correlated with improvements in insulin-stimulated AktSer473 phosphorylation after EPS (r = -0.679, P = 0.004)., Conclusions: Our data demonstrated that EPS induces more fused mitochondrial networks, which are associated with differential adaptations in mitochondrial dynamic processes in myotubes from lean humans and human with severe obesity. It also suggests that improved insulin signaling after muscle contractions may be linked to the reduction in Drp1 activity., (Copyright © 2020 by the American College of Sports Medicine.)

Dynamin-related protein-1 (Drp1) is a key regulator in mitochondrial fission. Excessive Drp1-mediated mitochondrial fission in skeletal muscle under the obese condition is associated with impaired insulin action. However, it remains unknown whether pharmacological inhibition of Drp1, using the Drp1-specific inhibitor Mitochondrial Division Inhibitor 1 (Mdivi-1), is effective in alleviating skeletal muscle insulin resistance and improving whole-body metabolic health under the obese and insulin-resistant condition. We subjected C57BL/6J mice to a high-fat diet (HFD) or low-fat diet (LFD) for 5-weeks. HFD-fed mice received Mdivi-1 or saline injections for the last week of the diet intervention. Additionally, myotubes derived from obese insulin-resistant humans were treated with Mdivi-1 or saline for 12 h. We measured glucose area under the curve (AUC) from a glucose tolerance test (GTT), skeletal muscle insulin action, mitochondrial dynamics, respiration, and H 2 O 2 content. We found that Mdivi-1 attenuated impairments in skeletal muscle insulin signaling and blood glucose AUC from a GTT induced by HFD feeding (p < 0.05). H 2 O 2 content was elevated in skeletal muscle from the HFD group (vs. LFD, p < 0.05), but was reduced with Mdivi-1 treatment, which may partially explain the improvement in skeletal muscle insulin action. Similarly, Mdivi-1 enhanced the mitochondrial network structure, reduced reactive oxygen species, and improved insulin action in myotubes from obese humans (vs. saline, p < 0.05). In conclusion, inhibiting Drp1 with short-term Mdivi-1 administration attenuates the impairment in skeletal muscle insulin signaling and improves whole-body glucose tolerance in the setting of obesity-induced insulin resistance. Targeting Drp1 may be a viable approach to treat obesity-induced insulin resistance., (© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

The purpose of this study was to determine whether intramyocellular glucose partitioning was altered in primary human myotubes derived from severely obese women with type 2 diabetes. Human skeletal muscle cells were obtained from lean nondiabetic and severely obese Caucasian females with type 2 diabetes [body mass index (BMI): 23.6 ± 2.6 vs. 48.8 ± 1.9 kg/m 2 , fasting glucose: 86.9 ± 1.6 vs. 135.6 ± 12.0 mg/dL, n = 9/group]. 1-[ 14 C]-Glucose metabolism (glycogen synthesis, glucose oxidation, and nonoxidized glycolysis) and 1- and 2-[ 14 C]-pyruvate oxidation were examined in fully differentiated myotubes under basal and insulin-stimulated conditions. Tricarboxylic acid cycle intermediates were determined via targeted metabolomics. Myotubes derived from severely obese individuals with type 2 diabetes exhibited impaired insulin-mediated glucose partitioning with reduced rates of glycogen synthesis and glucose oxidation and increased rates of nonoxidized glycolytic products, when compared with myotubes derived from the nondiabetic individuals ( P < 0.05). Both 1- and 2-[ 14 C]-pyruvate oxidation rates were significantly blunted in myotubes from severely obese women with type 2 diabetes compared with myotubes from the nondiabetic controls. Lastly, concentrations of tricarboxylic acid cycle intermediates, namely, citrate ( P < 0.05), cis-aconitic acid ( P = 0.07), and α-ketoglutarate ( P < 0.05), were lower in myotubes from severely obese women with type 2 diabetes. These data suggest that intramyocellular insulin-mediated glucose partitioning is intrinsically altered in the skeletal muscle of severely obese women with type 2 diabetes in a manner that favors the production of glycolytic end products. Defects in pyruvate dehydrogenase and tricarboxylic acid cycle may be responsible for this metabolic derangement associated with type 2 diabetes.

Healthy mitochondrial networks are maintained via balanced integration of mitochondrial quality control processes (biogenesis, fusion, fission, and mitophagy). The purpose of this study was to investigate the effects of severe obesity and type 2 diabetes (T2D) on mitochondrial network morphology and expression of proteins regulating mitochondrial quality control processes in cultured human myotubes. Primary human skeletal muscle cells were isolated from biopsies from lean, severely obese nondiabetic individuals and severely obese type 2 diabetic individuals ( n = 8-9/group) and were differentiated to myotubes. Mitochondrial network morphology was determined in live cells via confocal microscopy and protein markers of mitochondrial quality control were measured by immunoblotting. Myotubes from severely obese nondiabetic and type 2 diabetic humans exhibited fragmented mitochondrial networks ( P < 0.05). Mitochondrial fission protein Drp1 (Ser 616 ) phosphorylation was higher in myotubes from severely obese nondiabetic humans when compared with the lean controls ( P < 0.05), while mitophagy protein Parkin expression was lower in myotubes from severely obese individuals with T2D in comparison to the other groups ( P < 0.05). These data suggest that regulatory proteins in mitochondrial quality control processes, specifically mitochondrial fission protein Drp1 (Ser 616 ) phosphorylation and mitophagy protein Parkin, are intrinsically dysregulated at cellular level in skeletal muscle from severely obese nondiabetic and type 2 diabetic humans, respectively. These differentially expressed mitochondrial quality control proteins may play a role in mitochondrial fragmentation evident in skeletal muscle from severely obese and type 2 diabetic humans. Novelty Mitochondrial network morphology and mitochondrial quality control proteins are intrinsically dysregulated in skeletal muscle cells from severely obese humans with or without T2D.

Background/objectives: Impaired insulin-mediated glucose partitioning is an intrinsic metabolic defect in skeletal muscle from severely obese humans (BMI ≥ 40 kg/m 2 ). Roux-en-Y gastric bypass (RYGB) surgery has been shown to improve glucose metabolism in severely obese humans. The purpose of the study was to determine the effects of RYGB surgery on glucose partitioning, mitochondrial network morphology, and the markers of mitochondrial dynamics skeletal muscle from severely obese humans., Subject/methods: Human skeletal muscle cells were isolated from muscle biopsies obtained from RYGB patients (BMI = 48.0 ± 2.1, n = 7) prior to, 1 month and 7 months following surgery and lean control subjects (BMI = 22.4 ± 1.1, n = 7). Complete glucose oxidation, non-oxidized glycolysis rates, mitochondrial respiratory capacity, mitochondrial network morphology, and the regulatory proteins of mitochondrial dynamics were determined in differentiated human myotubes., Results: Myotubes derived from severely obese humans exhibited enhanced glucose oxidation (13.5%; 95% CI [7.6, 19.4], P = 0.043) and reduced non-oxidized glycolysis (-1.3%; 95% CI [-11.1, 8.6]) in response to insulin stimulation at 7 months after RYGB when compared with the presurgery state (-0.6%; 95% CI [-5.2, 4.0] and 19.5%; 95% CI [4.0, 35.0], P = 0.006), and were not different from the lean controls (16.7%; 95% CI [11.8, 21.5] and 1.9%; 95% CI [-1.6, 5.4], respectively). Further, the number of fragmented mitochondria and Drp1(Ser 616 ) phosphorylation were trended to reduce/reduced (0.0104, 95% CI [0.0085, 0.0126], P = 0.091 and 0.0085, 95% CI [0.0068, 0.0102], P = 0.05) in myotubes derived from severely obese humans at 7 months after RYGB surgery in comparison with the presurgery state. Finally, Drp1(Ser 616 ) phosphorylation was negatively correlated with insulin-stimulated glucose oxidation (r = -0.49, P = 0.037)., Conclusion/interpretation: These data indicate that an intrinsic metabolic defect of glucose partitioning in skeletal muscle from severely obese humans is restored by RYGB surgery. The restoration of glucose partitioning may be regulated through reduced mitochondrial fission protein Drp1 phosphorylation.

The Clinician Administered PTSD Scale (CAPS), originally developed as a diagnostic tool, is frequently used to evaluate treatment responses. Defining a case and measuring symptom changes are different processes that require different attributes for the instrument. Measuring symptom changes requires precision in measurement. Using the Rasch rating scale model, we evaluated this instrument for construct validity in a veteran sample. The distribution of the veteran measures did not align with the distribution of the item measures in the CAPS instrument. Separate analysis of the CAPS Frequency subscale and Intensity subscale were conducted. The Frequency subscale produced measures that encompassed the level of severity found in the veteran sample. Items from this instrument can be used to develop an equal interval scale to provide precise measurements for treatment evaluations and to identify clinical cut points for diagnostic purposes.